1. Field of the Invention
The present invention relates to the field of inductive devices, and more particularly to wire core inductive devices such as transformers, chokes, coils, ballasts, and the like.
2. Description of Related Art
It is common for low frequency application transformers and other inductive devices to be made up of a magnetic core comprising a plurality of sheets of steel, the sheets being die cut and stacked to create a desired thickness of the core. For many years, the thickness (thus number of necessary pieces) of the stampings has been determined by a strict set of constraints, e.g. magnitude of eddy currents versus number of necessary pieces. The individual sheets of selected thickness are oxide-coated, varnished or otherwise electrically insulated from one another in order to reduce/minimize eddy currents in the magnetic core.
The present inventor has developed wire core inductive devices such as transformers, chokes, coils, ballasts, and the like having a magnetic core including a portion of a plurality of wires rather than the conventional sheets of steel. The ends of the plurality of wires extend around the electrical windings and are arranged to substantially complete a magnetic circuit or flux path. These devices and related methods of manufacturing these devices are set forth in detail in U.S. Pat. Nos. 6,239,681 and 6,268,786, which are incorporated herein by reference. One important aspect of these devices is the provision of an increased operating frequency span enabling higher operating frequencies over conventional E/I type units. These increased operating frequencies approach those previously only efficiently and effectively reached by switch-mode power supplies, inverters, and converters which contained molded core type transformers.
A magnetic core of an inductive device will reach a magnetic saturation point when a sufficient magnetic force is applied to the core by current flowing through windings extending around the core. Saturation of the core is often a non-desirable condition because the inductance provided by the device drops drastically. In applications where a direct current component is present in a current flowing in a winding of an inductive device, the core will reach saturation more rapidly because the direct current component provides a magnetic bias.